Hot-dip-aluminizing alloy

ABSTRACT

An aluminizing alloy consisting essentially of about 0.75 to 4.0 percent manganese and the balance aluminum and impurities. The alloy when applied to a ferrous article by immersion of the ferrous article in a molten bath of the alloy providing a surface coating of higher brightness and uniform smoothness. The impurities may include up to 0.20 percent silicon, up to 0.35 percent iron and up to 0.02 percent copper. A composite article having a ferrous core and a coating of the aluminum base manganese alloy. A method of producing a hot dip aluminized ferrous article having a bright finish comprising providing a molten bath of an aluminum base alloy at about 1,250* to 1,400* F. and immersing a ferrous article in the bath for about 1 to 6 minutes. The aluminum base alloy consisting essentially of 0.75 to 4.0 percent manganese and the balance aluminum and impurities.

United States Patent Thompson 51 Feb.l,t972

[73] Assignee: Aluminum Company of America, Pittsburgh, Pa.

[22] Filed: July 22, 1969 [21] Appl. No.: 843,826

[52] U.S. Cl ..29/196.2, 75/138 [51] Int. Cl ..B23p 3/10 [58] Field ofSearch ..75/l38;29/l96.2

[56] References Cited UNITED STATES PATENTS 1,974,970 9/1934 Nock, Jr. ..75/l38 3,063,832 11/1962 Snyder 3,167,403 l/l965 Smith et al..

OTHER PUBLICATIONS Hansen, Constitution of Binary Alloys, 2d. Ed. Mc- Graw-I-Iill Book Co. N.(. 1958, pp. I10 1 l 1.

Primary Examiner-L. Dewayne Rutledge Assistant Examiner-J. Davis Att0rneyAmold B. Silverman [5 7] ABSTRACT An aluminizing alloy consisting essentially of about 0.75 to 4.0 percent manganese and the balance aluminum and impurities. The alloy when applied to a ferrous article by immersion of the ferrous article in a molten bath of the alloy providing a surface coating of higher brightness and uniform smoothness. The impurities may include up to 0.20 percent silicon, up to 0.35 percent iron and up to 0.02 percent copper. A composite article having a ferrous core and a coating of the aluminum base manganese alloy. A method of producing a hot dip aluminized ferrous article having a bright finish comprising providing a molten bath of an aluminum base alloy at about l,250 to l,400 F. and immersing a ferrous article in the bath for about I to 6 minutes. The aluminum base alloy consisting essentially of 0.75 to 4.0 percent manganese and the balance aluminum and impurities.

2 Claims, No Drawings HOT-DIP-ALUMINIZING ALLOY BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates to an aluminum alloy for use in ob taining through a hot-dip-aluminizing process an aluminumcoated ferrous article having superior brightness and uniform coating smoothness.

2. Description of the Prior Art The advantages of coating ferrous articles with other metals in order to obtain corrosion resistance and a durable attractive finish have long been known. It has been known to employ aluminum in effecting such a coating. One convenient means of accomplishing this is through immersion of the ferrous article in a molten bath of aluminum in order to obtain a uniformly bonded coating.

In the known hot-dip-aluminizing processes, the ferrous article, be it ironor steel, is first precleaned. The precleaning may be effected through such conventional means as grit blasting, alkaline cleaning, solvent degreasing or vapor degreasing. A second precleaning stage involving acid pickling in acids such as sulphuric, hydrochloric or hydrofluoric acids is then generally performed. The ferrous specimen is then exposed to a water rinse and subsequently is immersed in a suitable flux which may be at elevated temperatures. After fluxing, the specimen is dried and subsequently immersed in the molten aluminum bath. Upon removal from the aluminum bath any excess aluminum adhered to the ferrous article may be removed by mechanical action such as vibration or centrifugation. The composite-coated article may then be quenched or permitted to cool at ambient temperatures. See U.S. Pat. Nos. 2,738,289, 3,000,756 and 2,856,322.

The advantages of hot dip aluminizing become even more significant in connection with irregularly shaped objects which cannot be treated by some of the other conventional methods of applying aluminum to ferrous articles. Whether the article be irregularly shaped or be simply configurated, such as sheet material, a problem has been encountered in attempting to obtain an aesthetically pleasing coating of improved brightness. This problem has been compounded. by the need to obtain uniform smooth coating characteristics. Both of these objectives must be accomplished within the economic limitations imposed by the nature of the various products manufactured.

SUMMARY OF THE INVENTION This invention has solved the above-described problems by providing an alloy composition and a method of hot dip aluminizing employing the same to produce a composite aluminum-ferrous article having improved brightness. This is accomplished while providing uniform smooth surface coating characteristics.

The aluminizing alloy of this invention consists essentially of 0.75 to 4.0 percent manganese and preferably 0.75 to 1.15 percent manganese. The balance is aluminum and impurities which may include up to 0.20 percent silicon, up to 0.35 percent iron and up to 0.02 percent copper. Other impurities may be present in amounts up to 0.15 percent.

The composite article produced by hot dip aluminizing will have a core of ferrous material, an outer coating of an aluminum base alloy having a manganese content of 0.75 to 4.0 percent and an intermediate aluminum ferrous intermetallic compound.

The method of this invention contemplates providing a molten bath of this aluminum base manganese alloy at a temperature of about l,250 to l,400 F. and immersion of the ferrous article in the molten bath for about 1 to 6 minutes. The resultant product has a brightness superior to that of aluminum devoid of the manganese constituent.

It is an object of this invention to provide a hot-dip-aluminizing alloy and method of hot dip aluminizing which will yield an aluminized product having improved brightness and uniform coating smoothness.

It is another object of this invention to provide an aluminizing alloy which may be economically employed in hot dip aluminizing at a temperature range which does not produce detrimental effects on the resultant composite product.

It is another object of this invention to provide a hot-dipaluminizing alloy which may be employed in coating various types of ferrous materials and may be employed with materials pretreated in a conventional fashion.

These and other objects of the invention will be more fully understood and appreciated from the following detailed description which is exemplary and explanatory of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The hot-dip-aluminizing alloy of this invention contains a manganese constituent of about 0.75 to 4.0 percent with the balance being aluminum and impurities up to certain tolerable limits. The manganese content is preferably around 0.75 to 1.15 percent. It has been found that this alloy produces a substantial improvement in the surface brightness of the composite aluminum-ferrous article. The alloy, when applied by the method of this invention, produces a composite article having the desired uniform surface smoothness.

The impurities may generally include up to 0.20 percent silicon, up to 0.35 percent iron and up to 0.02 percent copper. It is preferred that the maximum silicon content be 0.15 percent, the maximum iron content be 0.30 percent and the maximum total of all other impurities be 0.15 percent with no individual other impurity exceeding 0.05 percent. It should be noted that where iron products are being hot dip aluminized the bath may have an increase in the iron impurity constituent as a result of bath pickup.'l"his might result in the iron impurity content exceeding the above recommended ranges, but under normal conditions the buildup will not be sufficient to be destructive of the advantageous brightening produced by the alloy of this invention.

In hot dip aluminizing, as provided herein, an increase in temperature of the molten aluminum bath beyond about 1,400 F. begins to produce a coating surface having undesirable roughness. It is therefore essential to the effective functioning of the product that the bath temperature not exceed 1,400 F. and it preferably should not exceed 1,350" F. It is, however, necessary to maintain the bath temperature sufficiently above the melting temperature of the alloy in order to insure adequate wetting of the ferrous. article by the molten bath. In the method contemplated by this invention the molten bath should be maintained at a temperature of at least l,250 F.

It has been found that no significant increase in surface brightness of the composite aluminum-ferrous article is obtained until the manganese constituent content reaches 0.75 percent. The maximum improvement in brightness is obtained by use of about 0.75 to 1.15 percent manganese. From 1.15 percent through 4.0 percent the brightness, while not quite as good as in the preferred range, nevertheless remains a substantial improvement over the same aluminum bath devoid of the manganese constituent in this range. If greater than 4.0 percent manganese, a high melting point constituent, is introduced into the bath, a peritectic phase relationship is established and the manganese constituent cannot be brought entirely into the solution without increasing the bath temperature. An increase in the bath temperature beyond the aboverecited ranges, however, results in a composite article which has an undesirable rough surface characteristic. The alloy of this invention, therefore, provides a maximum improvement in brightness within a range below a manganese constituent concentration which would produce the peritectic reaction.

In the process of this invention, a molten bath of the aluminum base manganese alloy of this invention is provided at a temperature of about 1,250 to l,400 F. and preferably 1,250 to l,350 F. The hot-dip-alurninizing alloy of this inven' tion may be provided either in the form of an ingot which is melted to provide a suitable bath or in the alternative it may be provided through the introduction of an appropriate amount of manganese into a bath of molten commercially pure aluminum. After suitable pretreatment the ferrous article is then immersed in the aluminum base manganese bath for about 1 to 6 minutes and preferably for about 1 to 3 minutes. As this immersion time is extended, the thickness of the layer of intermetallic aluminum-ferrous compound will be increased. Immersion for the periods recited herein, however, will have no detrimental effect upon the superior brightness and smoothness of the aluminum coating.

EXAMPLE In order to verify the superiority of the surface characteristics produced by the hot-dip-aluminizing alloy of this invention, several tests were made. A number of malleable iron cooking utensil handles were precleaned and fluxed in conventional fashion, then hot dip aluminized and subjected to conventional excess aluminum removal. The surfaces were then compared in order to determine the brightness and smoothness of the aluminized handles. Nine different bath compositions were employed. They were as follows:

Composition 3 A aluminum (99.75% pure) 3 A aluminum plus 0.24% manganese 3 A aluminum plus 0.48% manganese 3 A aluminum plus 073% manganese 3 A aluminum plus 0.94% manganese 3 A aluminum plus 1.15% manganese 3 A aluminum plus 3% manganese 3 A aluminum plus 4% manganese 3 A aluminum plus 5% manganese Three specimens were hot dip aluminized in each bath. The bath temperatures were maintained between 1,250 and 1,400 F. and immersion periods ranged from 1 to 3 minutes. The specimens processed in baths 1, 2 and 3 exhibited normal brightness and uniform smoothness. The specimens processed in baths 4, 5, 6, 7 and 8 exhibited substantially greater brightness than those processed in baths 1, 2 and 3 with the smoothness being about the same. The very best brightness was found in specimens processed in baths 4, 5 and 6, yet those processed in 7 and 8 rank only slightly below in brightness. The samples processed in bath 9 exhibited inferior brightness and an undesirable surface roughness.

These tests, therefore, confirm the production of a surface having superior brightness while maintaining the desired uniform surface smoothness with respect to the aluminizing alloy of this invention.

The aluminizing alloy of this invention and the composite product produced by the method of this invention not only have a surface characterized by improved brightness and uniform smoothness, but also produce a good uniformly bonded aluminum coating. Also, the alloy of this invention may be economically employed in a conventional hot-dipaluminizing process without the need for any departure from standard aluminizing practices, other than use of the specific alloy of this invention. It will also be appreciated that the method of this invention is adapted for use in batch, continuous or semicontinuous hot-dip-aluminizing processes. It is also adapted for use with a great variety of products of varying sizes and of both regular and irregular configurations.

As used herein, all percentages are expressed on the basis of weight of the total alloy.

Whereas particular embodiments of the invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

1 claim:

1. A composite metal article comprising a ferrous core and an aluminum base alloy coating applied b hot dip aluminizing, sai aluminum alloy consisting essentially of 0.75 to 4.0 percent manganese and the balance aluminum and impurities,

the surface of said composite metal article exhibiting a higher brightness than an aluminum-coated ferrous article devoid of said manganese,

the impurities include up to 0.20 percent silicon, up to 0.35

percent iron and up to 0.02 percent copper, and

the surface of said composite article exhibits uniform smoothness.

2. The composite metal article of claim 1 wherein the manganese content of said aluminum base alloy coating is about 0.75 to 1.15 percent, the maximum silicon content is 0.15 percent, and the maximum iron content is 0.30 percent, and

the maximum total of all other impurities is 0.15 percent. 

2. The composite metal article of claim 1 wherein the manganese content of said aluminum base alloy coating is about 0.75 to 1.15 percent, the maximum silicon content is 0.15 percent, and the maximum iron content is 0.30 percent, and the maximum total of all other impurities is 0.15 percent. 